It is known that bisphenols can be prepared by condensation of phenols with carbonyl compounds, biscarbinols, dienes or alkines by a large number of processes (in this context, see, for example, U.S. Pat. No. 2,191,831; U.S. Pat. No. 2,845,464; German Pat. No. 1,242,237; U.S. Pat. No. 3,073,868; U.S. Pat. No. 3,673,262; French Pat. No. 1,374,477; U.S. Pat. No. 3,394,089; and German Offenlegungsschrift No. 2,422,532). Where highly pure bisphenols are desired for use in the preparation of polycarbonates, special procedures for the process or subsequent expensive purification steps are required (in this context, see, for example, U.S. Pat. No. 3,049,568; German Pat. No. 1,186,874; German Pat. No. 1,168,445; Italian Pat. No. 650,774; German Offenlegungsschrift No. 2,359,500; German Offenlegungsschrift No. 2,364,164; and German Offenlegungsschrift No. 2,537,027.
The reason for these special procedures and for the expensive purification steps is that in general only highly pure bisphenols can be employed for the preparation of high-molecular thermoplastic polycarbonates (see, for example, German Pat. No. 1,186,874 or German Offenlegungsschrift No. 2,537,027.
Even according to German patent application No. P 28 11 182.2, which does not constitute a prior publication, a crystallization stage is a prerequisite to further use of the bisphenols for the preparation of polycarbonates, and in particular, a crystallization stage in the exchanger resin bed used for the preparation of the bisphenols.
It was thus surprising that high-molecular, thermoplastic polycarbonates of good quality are obtainable from crude bisphenols--preferably crude bisphenols possessing at least 2 alkyl substituents, and in particular, 4 alkyl substituents--by known processes for the preparation of polycarbonates, i.e., the phase boundary polycondensation process, without maintaining particular reaction conditions. The fact that the starting materials for the preparation of the polycarbonates, namely, the crude bisphenols, are obtainable in a particularly simple manner is regarded as a special advantage of the process.